In a dynamic rigid disk storage device, a rotating disk is employed to store information. Rigid disk storage devices typically include a frame to provide attachment points and orientation for other components, and a spindle motor mounted to the frame for rotating the disk. A read/write head is formed on a “head slider” for writing and reading data to and from the disk surface. The head slider is supported and properly oriented in relationship to the disk by a head suspension that provides both the force and compliance necessary for proper head slider operation. As the disk in the storage device rotates beneath the head slider and head suspension, the air above the disk also rotates, thus creating an air bearing which acts with an aerodynamic design of the head slider to create a lift force on the head slider. The lift force is counteracted by a spring force (often referred to as “gram load”) of the head suspension, thus positioning the head slider at a desired height and alignment above the disk which is referred to as the “fly height.”
A load beam is typically used to support the head slider via a gimbal region of a flexure mounted to the load beam, with the load beam including a mounting region at a proximal end, a rigid region at a distal end, and a spring region between the rigid region and the mounting region for providing the spring force creating the gram load. Head suspensions are normally combined with an actuator arm or E-block to which the mounting region at the proximal end of the load beam is mounted with a base plate so as to position (by linear or rotary movement) the head suspension, and thus the head slider, with respect to data tracks of the rigid disk. An alternative mounting arrangement (with which the present invention may be used) omits the base plate in a Unamount type mounting, available from Hutchinson Technology Inc. of Hutchinson, Minn., the assignee of the present invention.
The flexure typically includes the gimbal region having a slider bond pad to which the head slider is attached. The flexure provides a resilient connection between the slider and the load beam, and permits pitch and roll motion of the head slider as it moves over the disk in response to fluctuations in the air bearing caused by fluctuations in the surface of the rigid disk. Head suspension flexures can be provided in numerous ways, including designs in which the load beam and flexure are formed integrally with one another (a two-piece design comprising the base plate and the integral load beam/flexure) and designs in which the flexure is a separate piece from the load beam (a three-piece design comprising the base plate, the load beam and the separate flexure). Another form of head suspension with which the present invention may be used is a four piece design including a load beam, flexure, base plate, and hinge piece or spring layer.
One three-piece design includes a flexure having a resilient tongue and two resilient spring arms or gimbal arms. The head slider is supported on the resilient tongue (i.e. the slider bond pad), which is in turn supported by the spring arms (not to be confused with the spring region at the proximal or mounting end of the load beam). The spring arms are connected to a flexure mounting region, which is in turn connected to the load beam. The gram load provided by the spring region of the load beam is transferred to the flexure via a dimple contact that (typically) is located between the rigid region of the load beam and the flexure. Alternatives to the dimple (with which the present invention may be used) includes an etched tower or a ball made of suitable material such as glass. As used herein, the term “dimple contact” refers to any of these alternatives or other alternatives that provide the locating and pivoting function provided by the dimple. The spring arms allow the tongue of the flexure to gimbal (or rotate) in pitch and roll directions to accommodate surface variations in the spinning magnetic disk over which the slider is flying. The spring arms also force a return of the gimbal to a nominal position in the absence of external forces. The roll axis about which the head slider gimbals is a central longitudinal axis of the head suspension. The pitch axis about which the head slider gimbals is perpendicular to the roll axis. That is, the pitch axis is transverse to the longitudinal axis of the load beam, and crosses the roll axis at or around the head slider.
When the head suspension is not actually flying over a spinning disk in a “dynamic attitude,” the loaded state of the head suspension can be simulated by applying a force in the same direction as the air bearing force at a point on the head suspension other than on the slider bond pad where the head slider would be attached (or, if the slider is attached, other than to the head slider). This force is applied to lift the slider bond pad to its loaded position at the fly height. The orientation or attitude of the slider bond pad under this simulated loaded state is referred to as “static attitude.” The difference or bias between the dynamic attitude and the static attitude can be measured for a given head suspension so that a measurement of the static attitude, which can be an easier measurement to make than dynamic attitude, can be used to determine dynamic attitude for a given head suspension. In other words, a head suspension typically has a predetermined static attitude that can be used to assess the dynamic attitude of a head slider attached to the head suspension during normal operation of a disk drive.
Static attitude of a head slider bond pad can be measured with reference to pitch and roll axes of the head suspension. It has been found desirable to adjust the static attitude of a head suspension from a nominal orientation to impart a desired pitch and/or roll bias into the head suspension. In so far as these biases represent incremental changes in pitch and roll static attitude imparted to the head suspension, these too can be viewed as pitch and roll corrections, and the differences between nominal and desired attitude can be referred to as pitch and roll errors.
Because of the importance of correct head slider attitude, various methods exist for correcting pitch and roll errors to obtain appropriate static attitude. Such methods are disclosed in, for example, U.S. Pat. No. 5,682,780, issued Nov. 4, 1997 to Girard for “Gram Load, Static Attitude And Radius Geometry Adjusting System For Magnetic Head Suspensions”; U.S. Pat. No. 5,608,590, issued Mar. 4, 1997 for “Gimballing Flexure With Static Compensation And Load Point Integral Etched Features”; and U.S. Pat. No. 5,729,889 issued Mar. 24, 1998 for “Method Of Mounting a Head Slider To a Head Suspension With Static Offset Compensation”; and U.S. Pat. No. 5,832,764, issued Nov. 10, 1998 to Girard for “Method for Adjusting Gram Load, Static Attitude And Radius Geometry For Magnetic Head Suspensions.” Each of these patents is commonly owned by the assignee of the present application and each is fully incorporated herein by reference for all purposes.
One method of correcting errors in the static attitude involves mechanically twisting and/or bending the head suspension to alter the profile of the load beam. In such a method, the profile of the load beam can be altered to support the flexure at an attitude to the disk surface that compensates for any errors in the static attitude of the head suspension. That is, the load beam can be bent about an axis perpendicular to the longitudinal axis of the load beam to account for pitch errors in the static attitude of the head suspension. The load beam can also be twisted about its longitudinal axis to account for roll errors in the static attitude. Adjusting the head suspension in these ways, however, can negatively affect other head suspension parameters, such as the fly height, gram load, and overall resonance profile of the head suspension. In particular, bending the head suspension to affect pitch static attitude also affects gram load, resonance, and head lift height, while twisting the head suspension to correct roll static attitude affects head suspension resonance and introduces vibratory motion in the off-track direction, which can negatively impact disk drive performance. Such mechanical adjustments can also be undesirable due to the amount of forming required to get an appropriate adjustment in static attitude.
As disk drives are designed having smaller disks, closer spacing, and increased storage densities, smaller and thinner head suspensions are required. These smaller and narrower head suspensions are susceptible to damage if the disk drive is subjected to a shock load or if the suspension experiences excessive pitch and roll motion. Moreover, as the use of portable personal computers increases, it is more likely that head suspensions in these portable computers will be subjected to shock loads. Thus, it is becoming increasingly important to design the head suspension so that it is less susceptible to excessive movements caused by shock loads and by pitch and roll motion, while still maintaining the necessary freedom of movement in the pitch and roll directions. In this manner, damaging contact between the head slider and the disk surface and permanent deformation of components of the head suspension can be prevented.
Mechanisms, referred to herein as “limiters” have been developed for limiting the movement of a free end of a cantilever portion of a flexure for protection against damage under shock loads. Limiters can be located proximal or distal of the gimbal portion of the head suspension, or at any location in between. While the limiters provide valuable protection against damage, they can also restrict or prevent adequate range of movement for pitch and roll adjustment of the head suspension, because of the restriction on movement permitted by the limiters. It is to be understood that the present invention may be practiced without impairing the operation of limiters when present in the suspension being adjusted.
The present invention relates to adjustment of pitch and roll parameters for head suspensions with limiters useful in disk drive applications, particularly head suspensions which have limiters which provide a limited range of movement of a gimbal on which a head slider is mounted. The present invention may be used with designs which use multiple (e.g., leading and trailing) limiters. It is, of course, known that the size of head suspensions is continually being reduced. The combination of reduced size with multiple limiters presents difficulty in using prior art approaches for the adjustment of pitch and roll parameters for the gimbal. In one prior art approach, a pair of pins were used to adjust pitch, however with reduced size dual limiter designs, this prior art approach sometimes caused unhooked or damaged or deformed limiters and sometimes was not feasible simply because of space constraints.
The present invention overcomes shortcomings of the prior art by providing apparatus and method to adjust pitch and roll of the gimbal arms in a head suspension using three elements mechanically contacting one gimbal arm with the two elements on one side of the arm and the third element on the other side of the arm.
Determining the amount of adjustment necessary to correct the pitch and/or roll errors can be accomplished by referencing stored adjustment data describing the relationship between the amount of correction obtained for a given deformation using the present invention. In one aspect, the amount of adjustment needed is first determined, and the amount of deformation necessary to compensate for pitch error and/or roll error is predicted using statistical analysis. The prediction can be made by consulting stored adjustment data describing the relationship between the results achieved based on the amount of deformation. A response factor may be calculated for static attitude parameter adjustment. The response factor is a ratio between the resulting (estimated) deformation for the amount of actual deformation imposed on the spring arm or arms. The amount of actual deformation can be upwardly or downwardly adjusted based upon the actual results obtained using the response factor.
In another aspect, a model of the relationship between changes in a given static attitude parameter and the associated amount or extent of bending required may be stored in a computer. After the then-current parameter of the suspension is measured, the computer calculates the required correction (i.e., the difference between the measured and desired parameter values). The computer then accesses the model as a function of the required correction to determine the amount of actual adjustment needed to achieve the correction. Once the actual adjustment has been made, the parameter value may again be measured and used to update the model. Measured data from a given number of the most recently executed adjustments may be used to recompute the model.